1. Field of the Invention
The invention generally relates to ceramic materials.
2. Description of Related Art
The synthesis of materials with nanoscale dimensions is one of the most sought after technologies today, as particle size reduction has been postulated to lead to dramatic changes in physical properties. For example, typical ferromagnetic materials exhibit superparamagnetic behavior at particle sizes of 10-15 nm (Cao et al., “Controlling the particle size of amorphous iron nanoparticles,” J. Mater. Res., 10, 2952 (1995). One of the most pressing technology needs today is to find more efficient ways to store and process digital information. One of the possibilities to squeeze more data onto storage devices is by making the currently used magnetic nanoparticles even smaller. Similarly, nanosized superconductors could be used as an active component of novel nanocomposites with advanced useful properties and as principal building blocks of nanoelectronics as well as elements of solid-state quantum bits (qubits) (Schmidt, The Physics of Superconductors [Springer-Verlag, Berlin, 1997]). There are currently very few processes available, which can reliably produce nanomagnetic, semiconducting, or superconducting materials of desired sizes under mild conditions.
Most transition metal-based polymers reported to date do not contain units for conversion to a thermoset and thus afford low char yields at elevated temperatures. Carboranylenesiloxanes are highly sought after high temperature, thermally and thermo-oxidatively stable polymers (Dvornic et al., High temperature Siloxane Elastomers; Huthig & Wepf: Heidelberg, Germany (1990)). These materials are desirable, especially when it comes to their thermo-oxidative stabilities at very high temperatures. The introduction of unsaturated cross-linkable units such as a diacetylene unit in such materials resulted in the production of extended polymer networks of carboranylenesiloxanes (Henderson et al., “Synthesis and Characterization of Poly(carborane-siloxane-acetylene),” Macromolecules, 27(6), 1660 (1994)).
Spintronics: Spintronics (spin transport electronics or spin-based electronics) is a conceptual technology wherein the spin of an electron rather than its charge carries information ((a) Datta et al., Appl. Phys Lett., 56, 665-667 (1990); (b) Wolf et al., Science, 294, 1488-1495 (2001); (c) von Molnar et al., Proceedings of the IEEE, 91, 715-726 (2003)). This offers opportunities for a new generation of devices that combine standard microelectronics with spin-dependent effects that arise from the interaction between the spin of the carrier (electron) and the magnetic properties of a material. If the spin degree of freedom is used alone or is added to conventional semiconductor charge-based electronics, it will substantially increase the capability and performance of electronic products. The advantages of such products would be nonvolatility, increased data processing speed, decreased electric power consumption, and increased integration densities compared with conventional semiconductor devices.
Recently in the area of spin-polarized electronic transport, the giant magnetoresistance effect (GMR) has rapidly transitioned from discovery to commercialization for applications in magnetic information storage (Prinz, Science, 282, 1660-1663 (1998)). GMR is a quantum mechanical effect observed in layered magnetic thin-film structures that are composed of alternating layers of ferromagnetic and nonmagnetic layers (Baibich et al., Phys. Rev. Lett., 61, 2472-2475 (1988)). When the magnetic moments of the ferromagnetic layers are parallel, the spin-dependent scattering of the carriers is minimized, and the material has its lowest resistance. When the ferromagnetic layers are anti aligned, the spin-dependent scattering of the carriers is maximized, and the material has its highest resistance. The directions of the magnetic moments are manipulated by external magnetic fields that are applied to the materials. These materials can now be fabricated to produce significant changes in resistance in response to relatively small magnetic fields and to operate at room temperature.
Magnetic semiconductors: Magnetic semiconductors are materials in which components exhibiting both ferromagnetism (or a similar response) and useful semiconductor properties are present in a single material (FIG. 8). If implemented in devices, these materials could provide a new type of control of conduction. Whereas traditional electronics are based on control of charge carriers (n- or p-type), practical magnetic semiconductors would also allow control of quantum spin state (up or down). This would theoretically provide near-total spin polarization (as opposed to iron and other metals, which provide only ˜50% polarization), which is an important property for spintronics applications, e.g. spin transistors.
In normal, nonmagnetic conductors, electronic energy does not depend on the spin direction. It is not possible to distinguish between spin-up and spin-down electrons. In magnetic semiconductors, the d electrons of the magnetic ions influence the s and p electrons, and the conduction and valence band are split depending on the spin direction (Zeeman splitting) (adapted from Ando, Science, 312, 1883-1885 (2006)).
The search for materials containing ferromagnetic and semiconducting properties has been a long-standing and challenging one because of the need to balance the differences in crystal structure and chemical bonding in such materials ((a) Tanaka, J. Crystal Growth, 201/202, 660-669 (1999); (b) Prinz et al., Phys. Today, 48, 24 (1995)). A recent surge in a worldwide effort to create all electronic semiconducting spintronic devices occurred pursuant to the seminal discoveries of Ohno ((a) Ohno et al., Appl. Phys. Lett., 69, 363-365 (1996); (b) Ohno, Science, 281, 951-956 (1998)) and Awschalom (Kikkawa et al., Science, 277, 1284-1287 (1997)) and coworkers which demonstrated ferromagnetic Curie temperatures (Tc) in excess of 100K in (Ga, Mn)As, a diluted magnetic semiconductor, and spin coherence times greater than nanoseconds in a variety of technologically important semiconductors. Bulk metallic magnets derived from doping of the narrow-gap insulator FeSi with Co have exhibited GMR and high anomalous Hall conductance similar to that of (Ga,Mn)As (Manyala et al., Nature Materials, 3, 255-262 (2004)). The Fe0.9Co0.1Si was found to be nine times more resistive than Fe0.1Mn0.9Si and nearly 20 times more resistive than MnSi. Thus, various silicides such as Fe0.9Co0.1Si and Fe0.1Mn0.9Si, etc. promise to be exciting materials with magnetic and semiconducting properties.
Most of these silicides have been made by doping of known semiconductors (Manyala et al., Nature Materials, 3, 255-262 (2004)), by heavy ion irradiation of layered materials (Srivastava et al., J. Phys. D. Appl. Phys., 39, 1465-1471 (2006)) or by high pressure synthetic methods ((a) Kimura et al., Mat. Res. Soc. Symp. Proc., 646, N5.38.1-N5.38.6 (2001); (b) Ono, Photon Factory Activity Report, #23 Part B, 188 (2006)).